Wednesday, January 25, 2012

City Blocks: The Spaces In Between

A reader recently emailed me with an interesting question:

"While I have a good sense of the design elements of the narrow street and attached housing for the front, I don't see much of what the back looks like. Is it better to only have windows on one side and have a separate residence with another shared wall, This seems the most effective but do people want sunlight from both sides? Are they using private backyards, an alley, or both together? ... Are there shared courtyards and should these have grass? Isn't that similar to 'green space'.

The story of what has taken place in the spaces between blocks is an unexplored chapter of urban history. Every now and then particular episodes have been covered, with writers generally critiquing the process by which open space in block interiors yielded to new buildings.

Lewis Mumford in The City in History described, with disapproval, the process by which rear yards in medieval cities were filled in with houses and apartments as urbanization intensified in the late middle ages. Haussman has been criticized for permitting landlords to construct "airless and crowded tenements" behind the elegant street facades of new Parisian apartment buildings. Others have lamented Barcelona's failure to maintain the interior of blocks in the Eixample as green space. Even the modest concept of the mid-block laneway house has become a subject of controversy.

The process of block subdivision, infill and densification isn't an aberration, however, but instead represents the basic engine of urbanization in all times and places, at least where the process is not stunted or halted entirely by regulation. It is more noticeable when it occurs in the context of an idealized plan, such as Haussman's for Paris or Cerda's for Barcelona, but the same process is at work in thousands of other less noteworthy cities.

A 1615 drawing of Paris shows the process well: the blocks outside the old city walls, to the left, are thinly lined with rowhouses backing onto ample gardens, while inside the wall, blocks once similar have been carved into much smaller pieces by narrow streets until, at farthest right, interior garden space has almost vanished.

To return to the question that was posed, what is happening to the interior of the blocks during this process? In the unplanned city, the process of subdivision generally proceeded until an optimal ratio was struck between streets and accessible block space. Driving the process is the principle of maximization of land value, where a new street was justifiable only to the extent it increased adjacent land values in excess of the space lost to right of way, bearing in mind that ground floor, street-front rents are almost invariably command rents much higher than those on any other floor.

The result, in almost all cases, was a proliferation of small, or at least narrow blocks, generally not much more than 150 feet wide, and frequently a lot narrower. The image below of Bordeaux shows the end result of this process, with the block partially outlined in yellow, for scale, measuring 115' by 380':

With blocks of this width, few apartments are entirely buried within block interiors, lacking street-facing windows or exits, while light shafts admit sunshine to inward-facing rooms. There are no rear alleys and no yards, yet most apartments do receive natural light from at least two directions. Larger blocks frequently incorporate interior courtyards.

The same pattern can be imitated by planners, as in the case of Taipei, with the outlined block, one of the largest in this neighborhood, measuring only 75' by 200', with a small space left between back-to-back apartments. Streets are generally about 16' wide, with wider arterials at intervals. The amount of street frontage within a five-minute walk of this block must be phenomenal, providing a resident with access to many dozens of businesses steps away from his front door.

Due land value gradients, block size in the unplanned city generally shrinks toward the center. With planned cities, the opposite pattern is often seen, due to a tendency for grid-makers to overscale city blocks at the outset. leaving too much space too far from the street grid (a decision compensated for, in some places, by the introduction of alleys). Mexico City and Salt Lake City were laid out centuries apart, but in both cases a clear transition toward much smaller blocks is evident beyond the original gridiron as the economic picture came into clearer focus and the benefits of narrower blocks became more evident: in Salt Lake City (below right), from 720' to 380' square blocks, and in Mexico City from blocks 270' wide to 120' wide:

Ultimately, the question of what is going on between blocks depends in large degree on the size and shape of the blocks themselves, and that is a topic on which the experience of cities from around the world have a lot to teach us.

11 comments:

1. Row houses and tenements that begin to fill up their blocks need access to natural light to remain desirable. Air shafts are common between San Francisco victorians and between Old Law New York tenements. A thin column of space would be reserved between buildings that run together on the street face. About halfway back in the lot this column would provide windows into both buildings for light and air circulation. More modern designs require these columns to run all the way out to the street for emergency egress, creating the New Law tenement with inhabited "fins."

2. A very desirable housing form in places like London and Mexico City is the mews. A mews is a narrow (10' to 30') dead-end pedestrian street penetrating into an excessively wide block. Townhouses or apartments are built on both sides and the residents treat the street as a shared interior courtyard. There is usually a gate blocking street traffic and I almost never see a car parked inside though the original London design evolved from downstairs carriage houses below modest single family homes. A mews can be a key organizing tool to evolve better living space in blocks in the modern city, though it does not offer the retail and community possibilities of opening new narrow through streets.

3. In your Salt Lake City photo, the neighborhoods to the north (bottom) are the original residential "Avenues" laid out by Brigham Young in the 1840s and 1850s. The larger blocks to the south (top) came later over land originally designated as agricultural. There are about 250 of the larger 750' blocks and most of them have been subdivided, often multiple times, with small streets (40' wide typically, where the regular street is 130'). The streetcar suburbs of the early twentieth century are not in this photo, but were built with a smaller block size, but arranged along the same grid.

4. Most of your Mexico City photo was built in the same decades as the blocks of the Salt Lake City photo. You observe they were laid out "centuries apart" and the pattern of Mexico City streets alternating 40' and 60' in a grid was indeed set after the disastrous floods of the 1450's (fifteenth century hypertrophism?). The Doctores neighborhood pictured with its long narrow blocks was built at the end of the nineteenth century. From the 1400's to the 1800s, the typical surviving block was built about 300' square. Twentieth century blocks in Mexico City average around 200' by 600' but in a chaotic city of 20 million there is much variety.

5. I don't see any reliable pattern of developing toward smaller blocks over time in Mexico City or Salt Lake City. There is development from square to rectangular blocks, though.

Brian -- thanks for the comment. Are you sure about that sequence of development for Salt Lake City? The small-block neighborhood shown in the aerial is the old 20th Ward, while Wards 1-18 were composed of the larger block sizes and hosted most of the significant public and religious buildings, including the courthouse, the city hall and the temple. An 1860 city map shows Ward 20 as vacant land without streets:

In any event, it does not appear that blocks of those dimensions (700'+) were ever used again on a large scale in the city's growing suburbs, and as you note even those which were platted have since been broken down into smaller pieces.

As for Mexico City, the comment about being "centuries apart" was in regards to the original plat, which in MC occurred in the 16th century (not sure how much of the Aztec plan survived), while SLC's occurred in the mid-19th. I'm not claiming to have done a scientific study of block dimensions, but it seemed apparent, from a random selection of several newer neighborhoods around the historic center and futher out, that the typical newer block -- measuring from building face to building face -- had decreased from 270' to around 130'-170', although there are many 100' or less, particularly in the areas which originated as squatter settlements. The very newest townhouse lots on the far fringes of the city measure in at 60', the same width as the streets separating them!

The discussion on "as-needed" block subdivision was very interesting. Unfortunately this organic process of street addition is outlawed virtually everywhere today (except in shantytowns).

The comparison of block infill strategies across the world was also fascinating. After seeing the various kinds of "perimeter block" and courtyard-style buildings in Europe, I was amazed at how these useful residential typologies utterly failed to catch on in US cities, especially in New York.

New York suffered under the 'gloomy tenement + airshaft sliver' typology while rapidly-industrializing cities in Europe - Berlin, Barcelona, but NOT London - tended to have far better apartment buildings. True, many of the "Mietskaserne" in Berlin (and similar apartment buildings elsewhere in Central/Eastern Europe) saw their courtyards overrun with unpleasant uses (privies, loud workshops, massive laundry-drying operations), but by the early 20th century they had improved substantially: interior gardens and plazas frequently replaced the old noxious uses.

These "perimeter block" or courtyard-style buildings were often outfitted with enticing human-scale features that American rowhouse and tenement builders rarely bothered to provide: balconies, lavish mass-produced architectural figures and ornaments, ground-floor shops, street trees, etc. All these design features - along with the general separation of heavy industry from other uses, a practice that did NOT catch on in American cities until zoning was introduced - often resulted in an urban form that was far more pleasant and hospitable than contemporaneous US urban forms. I really think this was a major reason why Americans totally rejected - and fled - their tenement and rowhouse cities while Europeans didn't reject city life as a general proposition to nearly the same extreme.

Even today, the old Mietskaserne in Central/Eastern Europe are incredibly charming. Even if dilapidated and battered (they age very gracefully), you can tell many residents find the blocks comfortable: flowerpots and greenery spill forth from all the balconies (I almost never see flowers spilling forth from all those utilitarian NYC fire escapes), old ladies tend to little gardens, bikes, chairs, and other household objects clutter up the courtyards, men smoke, chat, and play games in the courtyard portals, children run around and play ball, little flashes of music and gentle chatter filter down to your ears as you wander through the maze of perimeter blocks, and so on. These humanizing elements of city life are often absent in even the "densest" of American cities/city blocks - most of Brooklyn's monotonous brownstone rows are eerily quiet!

@Marc: great point about the Mietskaserne! I did not feature them here, but if I can find a decent article on them I will have to run a follow-up post. There really was no equivalent to them in any American city, although here and there outside Manhattan a rough equivalent did appear:

Light shafts seemed to be disliked (wonder at what ratio they could make a come back). So I wonder what the right ground ratios are for alleys, backyards, and courtyards.

And for courtyards I wonder how it compares to the local plaza. What different uses can they have, how much shared space should you have in an area. Do you still need a plaza if every block has an interior courtyard?

Charlie, thanks for the NYC example! I was thinking the same thing: once you get to far northern Manhattan (around Washington Heights, say), to the Bronx, or to the outer reaches of Brooklyn, the tenements do indeed abandon the narrow "dumbbell" typology of lower Manhattan and take on a form that begins to resemble the courtyard-style apartment buildings of Europe. IMO they still fell fall short of the Mietskaserne though.

One of their shortcomings is the way the "green space" is/was treated. The air shafts of lower Manhattan were just useless scraps of mandated leftover space, and so too are the open spaces between these apartment buildings just mere leftover space. As is so typical of American "urban" design, it looks like bits of ersatz "wilderness" were dropped in between the apartment blocks - look but don't touch! The courtyards of the Mietskaserne, on the other hand, were consciously, overtly designed to be *people-centric* places with people-centric furnishings.

Sure, some of the mini-lawns between these NYC apartment buildings have since been taken over/rebuilt/redesigned for human use (and better these than nothing), but the public realm between these apartment buildings is generally pretty poor and looks/feels/behaves like a deficient, bare minimum afterthought.

The 1860 dated map for Salt Lake was published in 1930. The Utah Historic Society archives show the city growing residential development straight east of temple square across the mouth of City Creek into the smaller blocks of the Avenues and northwest into Marmelade and Capitol Hill. The larger blocks, as specified in Brigham Young's Plat of Zion (based on Joseph Smith's earlier Plat of Zion, though Smith never saw Salt Lake City) were to be agricultural as they were on the fertile valley floor. The smaller blocks of the Avenues and Capitol Hill are on hilly ground with City Creek cutting a deep canyon between them. Property records show the large valley plots being assigned in the late 1850s and the hillside plots in the 1860s but the Church was assigning land long before secular authorities documented it.

By the 1880s, the business district had grown up on the four streets south of the temple on the larger blocks and agriculture had moved down past 900 South toward the Chase and Woodruff plots that later became streetcar suburbs, but that was not the plan.

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The Aztec plat of Tenochititlan in the 1460s after the last giant destructive flood and the construction of the great protective Nezahualcoyotl dike laid out all the principal streets of modern central Mexico City. Archaeological documentation of subway excavations, the stone bases of major buildings, canal routings, and other projects show that Cortes and his men tore down the Aztec temples and used the existing stone and foundations to remodel Mexico into a more Spanish style city with Aztec streets.

There's a nice pair of photos in Stewart Brand's How Buildings Learn of Boston from the air in 1860 and in 1981. The downtown street grid is exactly the same but every single building save one -- hundreds of them -- has been demolished and replaced. That's what happened to Mexico.

There's a twenty-foot wide seventeenth century biombo in the National Bank of Mexico art collection that's often on display with a detailed painting of every street and building in the center of Mexico City around 1680. You can see there one reason neither the grid nor the street widths ever changed. The canals and streets and their levels and widths were fixed around the 1460's and changing them would have cut off the aqueducts or blocked flood control. Today subsidence and motor traffic accommodations have required hydrography to be controlled with pumping and tunneling, though one of the major canals is about to get Bus Rapid Transit. I'd still prefer a canal.

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That's an ugly suburban shot you posted of outer Ecatepec, but there's even worse car oriented development out in Tula, Hidalgo. Nevertheless, those homes are two story townhouses close together with narrow streets and have only one car stall per household. That design is a twenty-first century development. It's still a big step up from USA suburbia. The rate of development out there has fallen as the city doesn't grow so fast anymore since the national birthrate dropped below replacement almost a generation ago.

Most of the twentieth century blocks are around 200' by 600' including the 40' to 60' streets to the midline. A shift to smaller blocks in the last few years out in Ecatepec is possible.

The Doctores neighborhood in your photo was built to a new layout in the late 19th century, just like Salt Lake City which is why I say they aren't centuries apart but simultaneous. When Mexico was laid out in the 1460's, Doctores was under three meters of water and not to be reclaimed for centuries. Three miles north you would find a fifteenth century grid.

One interesting question to ask is that while it is possible to increase density by infilling narrow blocks, is it good urban practice? Likewise while it is possible to increase density by building high rise apartments 50+ stories into the sky, I personally disagree with such design as it totally ignores the human scale. While having blocks hundreds of meters apart is too large for the human scale, is having blocks 50 meters and less apart too small?

This isn't an outright condemnation of such design, but an actual question. I like seeing these narrow streets on Google Street View, but how do people like living and being there? Let's not forget that as your Paris image shows, many of these "large" 80-100 meter blocks were designed and built prior to the automobile, and were infilled later on.